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The drum dryer is the equipment used to convert the solutions and suspensions into solids. The main purpose is to spread the liquid to a large surface area so that drying can occur rapidly.
Construction of Drum Dryer
It consists of a hollow steel drum of about 0.75-1.5 m in diameter and 2-4 m in length. It is heated usually by steam and rotated on its longitudinal axis. The external surface of the drum is polished. Liquid or slurry is placed as feed in a pan. The drum is partially dipped in the pan. The spreader is used to spread liquid film evenly on the roller. The rotation of the drum is adjusted so that all of the liquid is fully vaporized. The drum is rotated continuously. The dried deposit or material can be scraped off with the help of a Doctor’s knife. The dried material is collected in a storage bin.
Working of Drum Dryer
A drum rotates, the liquid material gets adhered to an external surface of a drum. The liquid is spread as a film onto the surface. The drying of the material is done by the process of steam when passed into the drum. By the mechanism of the conduction, the heat gets transferred into the drum, and the drying process takes place. The materials are completely dried during the whole process during its revolutions. The dried materials are scrapped by the knife and that falls into the bin.
Advantages of Drum Dryer
- Drying takes place in less time.
- It is suitable for thermosensitive drugs.
- It occupies less space.
- To reduce the temperature of drying the drum can be enclosed in a vacuum chamber.
- Rapid drying takes place due to rapid heat and mass transfer.
Disadvantages of Drum Dryer
- The maintenance cost is high.
- Skilled operators are essential to control the thickness of the film.
- It is not suitable for fewer solubility products.
- The operating conditions are critical. Therefore it is necessary to introduce careful control on feed rate, film thickness, speed of drum rotation, and drum temperature
- Drum dryer is used for drying of solutions, slurries, and suspensions
- Milk products, starch products, ferrous salts, suspensions of zinc oxide, suspensions of the kaolin, yeast, pigments, malt extracts, antibiotics, glandular extracts, insecticides, DDT, calcium, and barium carbonates are dried by this method.
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